Such a catalyst complex and the degradation method are known from WO2014/209117A1. The known complex comprises a magnetic nanoparticle, so as to enable a separation between the first aqueous phase and the second phase under the impact of an external magnetic field. The second phase contains catalyst complex, additives, oligomers, trimers and dimers. This second phase may be reintroduced in a first reaction step, wherein the polymer is degraded. The monomers can be retrieved by means of crystallisation. According to the said patent, a rather small size of 5-10 nm is optimal in terms of yield and recovery of catalyst complex. This recovery is carried out by applying an electro-magnetic field gradient, such as by an external magnet. Herein, a separation is made between a first phase comprising the solvent, added water and monomer and a second phase comprising catalyst complex, oligomers, trimers and dimers.
In further experiments with the catalyst complex, it has been found that the separation between the two phases is not perfect. A significant amount of catalyst complex tends to end up in the first phase that comprises the solvent, for instance ethanediol, and added water. This catalyst complex has to be removed and cannot be reused again. This is disadvantageous for the overall yield and commercial viability of the degradation treatment.